Science News

Study Bolsters Link Between Parkinson's Disease, Pesticide

Fungicide widely used in Valley found as a common factor in patients with disease

- Nov 16 2008

By Barbara Anderson

For years, researchers have suspected commercial pesticides put people at risk for Parkinson's disease. Now evidence in the San Joaquin Valley suggests it's true.

Researchers have found a strong connection between the debilitating neurological disease and long-term exposure to pesticides, particularly to a fungicide that is sprayed on thousands of acres of almonds, tree fruit and grapes in the Valley.

The fungicide ziram -- the 20th most-used agricultural toxin in California in 2006 -- emerged as a common factor in a UCLA study of 400 people with Parkinson's in the Valley.

"People exposed over a 25-year period to ziram have about a threefold increased risk of developing Parkinson's," said Jeff Bronstein, professor of neurology and head of the Movement Disorder Center at the University of California at Los Angeles.

More than 660,000 pounds of ziram were used on crops in Fresno, Kings, Madera, Merced, Tulare and Kern counties in 2006, the most recent year for which figures are available. About 1.3 million pounds of the fungicide were used statewide, according to the California Department of Pesticide Control.

The research showed the fungicide kills certain brain cells, and their death has been associated with Parkinson's, Bronstein said. Now that researchers have a better understanding of what happens when exposure occurs, the information could lead to treatments to prevent or slow the progression of Parkinson's disease, he said.

But it's too early to talk about restrictions or a possible ban, because state regulators have just become aware of the latest ziram research. The California Department of Pesticide Regulation has placed a high priority on assessing the risk of ziram, said Lea Brooks, assistant director of communications.

The association between a fungicide and Parkinson's could help explain why the disease appears to be more common among people in the agriculture-rich Valley than elsewhere in California. Researchers have long thought that's so, but no one knows how many people have Parkinson's disease.

A Parkinson's registry being developed at the Parkinson's Institute and Clinical Center in Sunnyvale will track the prevalence of the disease. It should reveal how widespread Parkinson's is statewide and where the Valley ranks.

Another UCLA study of death certificates showed a higher rate of Parkinson's deaths in areas that reported higher pesticide use, including the Valley. But researchers say death certificates don't capture the full story.

"No one knows the true incidence and prevalence of Parkinson's, and no one knows whether it's changing over time," said Dr. J. William Langston, a neurologist and director of the Parkinson's Institute.

A Parkinson's registry probably would find more cases of Parkinson's in the Valley than in other areas, said Dr. Abbas Mehdi, a Fresno neurologist.

"I'm quite convinced the environment is having quite a significant impact," Mehdi said, because there are too many patients for the size of the population.

Growers advocates say it's important to keep ziram use in perspective. Ziram isn't the most popular pesticide, said Barry Bedwell, president of the California Grape and Tree Fruit League. About 46 million pounds of sulfur -- the most common fungicide -- were used on all California crops in 2006. This is 40 times the amount of ziram that was applied.

"From our perspective, it would be great to let people know that the No. 1 pesticide used is an organic compound -- it is sulfur," Bedwell said.

And growers are as interested as anyone in making sure the chemicals used on crops are safe, Bedwell said.

"They live in these areas," he said. "These are their communities."

Farmworker advocates are not yet familiar with the details of the new ziram study, but in general, they are frustrated with pesticide safety regulations, said Erik Nicholson, national vice president with the United Farm Workers.

The regulatory process "completely ignores the long-term exposure to pesticides and their effects on human beings," he said. Ziram may be just another example, he said.

Parkinson's patients and their families in the Valley are eager for research to continue.

Sarah Osuna, 79, of Madera began having tremors and other Parkinson's symptoms about 15 to 20 years ago. She was "handed a hoe" at 14 and became a farmworker. She wonders whether years of exposure to pesticides triggered her disease. "It's a possibility, because I worked in the fields all my life," she said.

Osuna's daughter, Kathy Mendonca, 43, of Madera also wants to know whether the environment is to blame. Parkinson's has robbed her mother of so much, she said. She no longer can garden and cook and care for herself. "She falls a lot," Mendonca said.

The Valley is a logical place to study Parkinson's disease, said Beate Ritz, vice chair of the Department of Epidemiology at UCLA and director of the Occupational and Environmental Epidemiology Program.

The causes of Parkinson's disease remain unknown, but environmental factors, as well as genetics, are believed to be involved for people who develop the disease after age 50. Most Parkinson's patients get the disease as older adults. Genetics are believed to be more involved for people who get the disease at younger ages.

UCLA researchers began enrolling people in the Valley in the Parkinson's Disease, Environment and Genes study in 2001. In the past seven years, 400 Parkinson's patients have enrolled. Another 400 people without Parkinson's also participate.

The increased risk for Parkinson's from exposure to ziram was found by comparing where residents lived with pesticide-use reports. California requires commercial pesticide applicators to record when and where they sprayed crops and what was sprayed.

Researchers in the past had to rely on people's memories of when they had been exposed to pesticides, Ritz said. Pesticide-use reports are more reliable, she said.

Bronstein said the study breaks new ground by identifying an individual pesticide and suggesting how it increases the risk for Parkinson's.

The discovery of an association with ziram -- a commercial fungicide -- is a big step, he said.

Researchers aren't saying ziram exposure causes Parkinson's, Bronstein said. "That last absolute proof is going to take time," he said. And ziram is not the only pesticide or fungicide that needs further study, he said.

"We're not trying to get rid of pesticides," he said. "We're just trying to get rid of the bad ones or minimize exposure."

Ziram appears to be toxic to dopamine-producing cells, Bronstein said. A lack of dopamine, a chemical that sends signals to nerve cells, has been associated with Parkinson's disease. When researchers exposed the dopamine-producing cells to ziram, they died quickly, and mice exposed to the fungicide developed symptoms of Parkinson's within two weeks, he said.

Results of this study appeared in the September issue of the Journal of Biological Chemistry.

The study also showed that ziram interfered with a cell's ability to break down proteins. Once a protein's life cycle is over, it has to be eliminated or oxidized for cells to remain healthy. There is speculation that protein disorders may have something to do with Parkinson's, as well as Alzheimer's and other brain degenerative diseases.